1. Field of the Invention
The present invention relates to a novel slurry-phase method to produce mixed alcohols from synthesis gas by utilizing a nanosized catalyst. The catalyst is activated by nanosizing and sulfiding during catalyst preparation.
2. Discussion of the Prior Art
Synthesis gas, hereinafter xe2x80x9csyngasxe2x80x9d is produced from any organic/carbonaceous source, such as, but not limited to municipal solid waste (MSW), refuse derived fuel (RDF), biogas from a digester, sewage sludge, chicken manure, turkey manure, other animal and agricultural waste, corn stover, switch grass, timber, grass clippings, construction demolition materials, cotton gin waste, biomass, landfill gas, natural gas and the like. The catalytic production of mixed alcohols from synthesis gas is a well established route and the literature contains numerous examples pertaining to this transformation. Of particular interest is a method described in U.S. Pat. Nos. 4,675,344; 4,749,724; 4,752,622; 4,752,623; and 4,762,858, all originally assigned to Dow Chemical Company. These patents describe, in general, a micron-size supported catalyst based on molybdenum disulfide (MoS2). Mixed alcohols, primarily C1-C4, i.e. methanol-butanol, are produced in good yields when the Dow catalyst is used in a packed column or fluidized bed. The best yield of oxygenates fraction is approximately 20%, on a CO2-free basis, with up to 85% selectivity to mixed alcohols. The rate of 0.1-0.4 grams product/gram catalyst/hour is claimed by the use of the Dow catalysts at 240-325xc2x0 C. reaction temperature and 700-3000 psig. The above Dow patents and the references discussed and cited therein are incorporated by reference in this application.
Review of the above noted prior art and references will show that a process and catalyst that improves upon conditions of high temperature and high pressure conversion of synthesis gas to mixed alcohols, and which provides a higher conversion rate of synthesis gas to mixed alcohols per pass over/through the catalyst are highly desirable, especially for commercial applications.
For commercial application, a process that improves upon conditions of high temperature and high pressure and allows higher conversion per pass are highly desirable. To make a commercially significant alcohol process the catalyst must be highly efficient as well as the conditions in which the catalyst operates. The efficient catalyst must yield a high ratio of mass of product per given mass of catalyst in a given period of time. The catalyst must be stable and active over long periods of time before regeneration or replacement of the catalyst is required. When the feed gas has a low ratio, ideally when the H2/CO ratio is less than 2 to 1, the catalyst will be highly selective to produce a commercial product to avoid purification or removal and disposal of by-products with the addition of a distillation tower that will split the product into two or more product streams.
When the mixture is used as a neat fuel for automobiles the presence of C1 alcohol, i.e. methyl alcohol, is more beneficial than when the alcohols are used as a commercial blend in gasoline. As used in this application, the weight ratio of methanol or C1 alcohol to C2+alcohols means the higher alcohols, such as ethanol, propanols, butanols, etc., taken as a whole for calculation purposes. This number may be calculated by determining the weight fraction of methanol in the mixed alcohols. The esters or ethers portion of the alcohol mix are not included in either the C1 to C2+ numbers. It is therefore understood that it would be beneficial to prepare mixed alcohols, primarily C1-C4, from synthesis gas derived from any carbonaceous source. It would also be beneficial to produce mixed alcohols in a highly efficiently manner by a catalytic method, i.e. in high yield per pass to avoid gas recycle under mild conditions of temperature and pressure.
It is therefore an object of the present invention to prepare mixed C1-C4, alcohols, primarily from synthesis gas derived from any carbonaceous source.
It is therefore an object of the present invention to produce mixed alcohols in a highly efficient manner by a catalytic method, having a high yield per pass to avoid gas recycle under mild conditions of temperature and pressure.
The present invention provides a novel method for producing mixed alcohols by combining one or more of the following steps. First a catalyst is selected from the Group VI metals, namely Cr, MO, W and mixtures thereof Next, the selected metal is nanosized to a mean particle diameter (ND) of less than about 100 nm. Nanosizing the metal is an especially important feature of the present invention, in that nonosizing provides more surface area per unit volume of the metal, thereby enhancing the reaction rates. The nanosized metal catalyst is then sulfided to enhance its resistance to the catalyst poisons that are normally present in syngas.
Nanosizing of the metal catalyst can be achieved by a variety of methods. One preferred method of nanosizing is sonication of a carbonyl precursor of the metal. An example of nanosizing is found in the literature reference (Mdleleni er al. J. Amer. Chem. Soc. 120 6189-6190 (1998)). Catalyst-sulfiding can be achieved during or after the nanosizing procedure.
During the alcohol production from syngas production, the nanosized, sulfided Group VI metal catalyst may be unsupported, or it may be supported on a high surface area support such as carbon, alumina, silica or the like. In either arrangement the nanosized catalyst is suspended in an inert solvent, such as a high molecular weight hydrocarbon solvent such as ethylflo-164, to form a slurry. Suspension of the nanosized catalyst allows excellent heat management during the thermal operations, and this in turn increases mixed alcohol product yield.
The syngas is then passed through the catalyst slurry to produce alcohols in the product stream. The input syngas composition varies from H2/CO of 1/4 to 3/1 though other gaseous impurities may be present. In order to enhance reaction rates, additives that make the Group VI metal catalyst more susceptible to initial carbon monoxide attack are preferred. The operating temperature range is from about 200xc2x0 C. to less than about 300xc2x0 C. The operating pressure ranges is from about 500 to about 3000 psig. The space-time-yield (STY) of product mixed alcohols is better than those claimed by any known commercial methods, that is greater than about 0.4 gram product/gram catalyst/hr. In order to enhance catalyst life, a small amount of sulfur source is added either directly to the reaction vessel in which alcohols are being continuously produced, or to the incoming syngas stream.
By combining these steps, using a novel catalyst in a novel process efficiently produces mixed alcohols. In one embodiment of this invention, nanosized particles (MPD less than 100 nm) of molybdenum are produced by the sonication method and are suspended in a hydrocarbon solvent having a carbon chain length of 30. A sulfur source, being elemental sulfur itself, is added to the slurry. By contacting the slurry with a stream of carbon monoxide and hydrogen in 1/2 ratio at temperature in the range of about 250 to about 280xc2x0 C. and pressure in the range of about 500 to about 200 psig pressure, mixed alcohols are produced in the product stream with STY surpassing 0.4 grams product/gram catalyst/hour reported with the known prior art technology.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combination, and elements as herein described, and more particularly defined by the appended claims, it being understood that changes in the precise embodiments to the herein disclosed invention are meant to be included as coming within the scope of the claims, except insofar as they may be precluded by the prior art.